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A new file system feature called "Concurrent I/O" (CIO) was introduced in the Enhanced environments, particularly commercial relational databases. In many cases, the database performance achieved using Concurrent I/O with JFS2 is comparable to that obtained by using raw logical volumes. This paper details the implementation and operational characteristics of Concurrent I/O, and presents the results of our performance evaluation of Concurrent I/O with Oracle9i Database.
The file system has long been the heart of UNIX® storage management. Commands and interfaces for manipulating and managing data stored on files are commonly used throughout the UNIX world by users of all skill levels. Managing persistent data via such universally understood mechanics is key to application portability. File systems thus provide a very useful and desirable abstraction for data storage.
As is often the case with any method of abstraction, however, the use of file systems results in some tradeoffs between performance and ease of use. The fastest means of transferring data between an application and permanent storage media such as disks, is to directly access more primitive interfaces such as raw logical volumes. The use of files for data storage involves overheads due to serialization, buffering and data copying, which impact I/O performance. Using raw logical volumes for I/O eliminates the overheads of serialization and buffering, but also requires a higher level of skill and training on the part of the user since data management becomes more application-specific. Also, while file system commands do not require system administrator privileges, commands for manipulating raw logical volumes do. However, due to its superior performance, database applications have traditionally preferred to use raw logical volumes for data storage, rather than using file systems.
With the Concurrent I/O feature now available in JFS2, database performance on file systems rivals the performance achievable with raw logical volumes.
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